Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.30   11.116%   $95.8931   $95.89   $95.90   $95.90  
  Purchase #2 $92.71   10.694%   $102.6244   $102.62   $102.60   $102.60  
  Purchase #3 $35.38   11.145%   $39.3231   $39.32   $39.30   $39.30  
  Purchase #4 $225.62   5.379%   $237.7561   $237.76   $237.75   $237.80  
  Purchase #5 $110.66   12.798%   $124.8223   $124.82   $124.80   $124.80  
  Purchase #6 $110.25   5.789%   $116.6324   $116.63   $116.65   $116.60  
  Purchase #7 $7.92   4.814%   $8.3013   $8.30   $8.30   $8.30  
  7 purchase totals = $668.84       $725.3527   $725.34   $725.30   $725.30